Metal-Organic Frameworks (MOFs) have garnered significant interests in the last two decades due to their promising potential in many applications such as gas adsorption, separation, catalysis and sensing. For example, see Yaghi, O. M.; O'Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Nature 2003, 423, 705. (b) Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F. Acc. Chem. Res. 2005, 38, 217. (c) Horike, S.; Shimomura, S.; Kitagawa, S. Nat. Chem. 2009, 1, 695. (d) Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K. Nature 2000, 404, 982. (e) Jiang, H.-L.; Liu, B.; Akita, T.; Haruta, M; Sakurai, H.; Xu, Q. J. Am. Chem. Soc. 2009, 131, 11302. (f) Kreno, L. E.; Leong, K.; Farha, 0. K.; Allendorf, M.; Van Duyne, R. P.; Hupp, J. T. Chem. Rev. 2012, 112, 1105. (g) Yang, S.; Liu, L.; Sun, J.; Thomas, K. M.; Davies, A. J.; George, M. W.; Blake, A. J.; Hill, A. H.; Fitch, A. N.; Tang, C. C.; Schröder, M. J. Am. Chem. Soc. 2013, 135, 4954. (h) Bloch, E. D.; Queen, W. L.; Krishna, R.; Zadrozny, J. M.; Brown, C. M.; Long, J. R. Science 2012, 335, 1606. (i) Wang, Z.; Cohen, S. M. Chem. Soc. Rev. 2009, 38, 1315.
Compared with other porous materials such as zeolite and mesoporous silica, MOFs are based on crystalline porous structures tunable on the atomic scale, which can be designed and functionalized by judicious choice of metal nodes and modification of the organic linkers. However, one of the limitations of most MOFs is their low chemical stability, which undoubtedly hampers their application in industry. A rule of thumb for the construction of stable MOFs comes from the simple Hard and Soft Acid and Base Theory, which guides the selection of the metal-ligand combination for a MOF. For example, see Pearson, R. G. J. Am. Chem. Soc. 1963, 85, 3533. Because the carboxylate group is a hard Lewis base, hard Lewis acids such as Fe3+, Cr3+, Zr4+ and Ti4+ are usually considered good candidates for the construction of robust MOFs. This method has become the focus of some recent research efforts but very few stable MOFs have been obtained, especially in single crystal form. For example, see (a) Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. J. Am. Chem. Soc. 2008, 130, 13850. (b) Ferey, G.; Serre, C. Chem. Soc. Rev. 2009, 38, 1380. (c) Phan, A.; Doonan, C. J.; Uribe-Romo, F. J.; Knobler, C. B.; O'Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2010, 43, 58. (d). Murray, L. J.; Dinc{hacek over (a)}, M.; Yano, J.; Chavan, S.; Bordiga, S.; Brown, C. M.; Long. J. R. J. Am. Chem. Soc. 2010, 132, 7856. (e) Feng, D.; Gu, Z.-Y.; Li, J.-R.; Jiang, H.-L.; Wei, Z.; Zhou, H.-C. Angew. Chem. Int. Ed. 2012, 51, 10307. (f) Jiang, H.-L.; Feng, D.; Liu, T.-F.; Li, J.-R.; Zhou, H.-C. J. Am. Chem. Soc. 2012, 134, 14690. The main reason is that MOFs based on these metal ions of high valence are difficult to crystallize. Occasionally, MOFs in the form of crystalline powder were obtained, but structure solution and refinement based on Powder X-Ray Diffraction (PXRD) data is not straightforward. Furthermore, the incorporation of rarely reported metal nodes into MOFs is less predictable and controllable.
Metal-organic frameworks have many applications including, for example, in the field of adsorption, storage, separation or controlled release of chemical substances, such as, for example gases, or in the field of catalysis. Metal-organic frameworks may also be useful in the field of pharmaceuticals (controlled release of medicaments) and in the field of cosmetics.
There are in fact a growing number of applications for metal-organic frameworks and as such there is an ever growing need for new such materials with a variety of properties and a need for new metal-organic frameworks having improved properties.
In addition, there is a need to develop new processes for preparing metal-organic frameworks that allow for the preparation of a wide variety of metal-organic frameworks and/or improve the quality of the metal-organic frameworks obtained.
However, metal organic (framework) powder material has been prepared by various methods but prior to the present invention large single crystals of metal organic frameworks containing a number of different metal ions have not been prepared. In particular, monocrystalline and polycrystalline aluminium metal organic frameworks have not been prepared prior to the present invention. In fact, serious difficulties have been experienced preparing crystalline metal organic frameworks containing aluminium.
For aluminium MOFs, reports of successful preparations of aluminium MOFs are rare. In the literature, Ferey et al (Chem. Mater. 2009, 21, 5695-5697 & Chem. Mater. 2009, 21, 5783-5791) describe the preparation of aluminium MOFs (labelled as MIL-100, MIL-120, and MIL-121) using hydrothermal synthesis, which were also the subject of US patent application US2012/0055880 A1. The sizes of the crystals obtained were however relatively small. For example, US2012/0055880 reports crystal sizes ranging from 1 micron up to only 30 microns (0.001 mm to 0.03 mm). Ferey et al therefore fail to provide aluminium MOFs having a large crystal size.
In addition, U.S. Pat. No. 8,648,002 describes the preparation of an aluminium MOF. However, this MOF (MOF-53) is in fact amorphous and as a result exhibits very small particle size in the region of 350 manometers. U.S. Pat. No. 8,648,002 therefore fails to prepare an aluminium MOF which is crystalline, let alone which is polycrystalline or monocrystalline and having large crystal sizes.
All these references highlight that despite a significant effort to prepare aluminium MOFs exhibiting large crystal sizes and monocrystalline characteristics, all such attempts have failed. There are therefore clearly great difficulties associated with the preparation of aluminium metal organic framework materials having the desired properties.
In the case of aluminium MOFs, there is therefore a need to provide crystalline MOFs that exhibit a greater crystal size and a minimum degree of crystallinity. As well as providing crystalline products, there is also a need to provide MOFs in monocrystalline and polycrystalline form. A monocrystalline MOF (or a single crystal MOF) consists of a MOF in which the crystal lattice of the entire solid is continuous, unbroken (with no grain boundaries) to its edges. Monocrystalline is opposed to amorphous material, in which the atomic order is limited to short range order only. Polycrystalline materials lie between these two extremes; they are made up of small crystals. They are different from amorphous materials. Large single crystals are very rare in nature and can be difficult to produce in the laboratory.
Metal-organic frameworks are coordination polymers having an inorganic-organic hybrid framework that comprises metal ions and organic ligands coordinated to the metal ions. These materials are three-dimensional, e.g. they have three-dimensional lattices in which the metallic species are joined together periodically by spacer ligands.
An object of the invention, therefore, is to provide an aluminium based metal organic framework having a large crystal size. Another object is to provide a method of preparing monocrystalline and polycrystalline aluminium metal organic frameworks having a larger crystal size than previously achieved.